1. Field of the invention
The present invention relates generally to a display device such as a thin-film transistor (TFT) liquid crystal display device, and more particularly to a device for protecting a display device against the detrimental build-up of heat and the irradiation of light.
2. Description of the prior art
In recent years liquid crystal display devices of an active matrix type, which has thin-film transistors (TFT) with pixels of liquid crystal have become popular. This type of display device exhibits a higher gradation than a duty-drive type liquid crystal display, and the resulting image quality is almost equal to that reproduced by conventional CRT displays. When the image quality is the same, the active matrix crystal display is more advantageous than the conventional CRT displays in that the thickness and size of the active matrix crystal display devices can be easily reduced, thus saving electricity. These merits stimulate the industry's interest in the active matrix crystal display device.
Referring to FIG. 7, a typical example of the IC drivers used in the conventional TFT display devices will be described:
An IC driver 2 is supported by a tape carrier 1 which is coupled by an anisotropic conductive film (not shown) to the terminal electrodes of a liquid crystal panel 3.
This arrangement is not applicable to a high precision display device having a liquid crystal panel 3 which requires terminal electrodes to be arranged with pitches of 1OO .mu.m or less, because of the difficulty of accurately arranging the terminal electrodes of the tape carrier 1, and the low resolution of the anisotropic conductive film.
FIG. 8 shows an improved display device which has a liquid display section having substrates 12, and 13 with a liquid crystal 11 interposed therebetween. The substrate 12 includes wiring electrodes 14 disposed on an edge area thereof on which a IC driver 15 is provided by the Chip-on-Glass System (COG System). Electric welding is carried out by wire bonding or alternatively soldering, each of which requires that the wiring is made of metal capable of wire bonding or having good affinity with solder. The selected material is costly, thereby increasing the production costs of liquid crystal display devices.
The wiring electrodes 14 are joined to the electrodes of the IC driver 15 with an electrically conductive adhesive. However, the build-up of heat in the display device impairs the constant resistivity of the joined electrodes, particularly at such a relatively high temperature such as when analog signals are treated. The build-up of heat also causes the malfunction of the IC driver 15.
The IC driver 15 includes a circuit as shown in FIG. 9. The image signal applied to a terminal 21 is stored in a sampling capacitor 23 in response to the input of a sampling pulse supplied to a gate transistor 22. When a transfer (TRF) signal applied to another gate transistor 24 is amplified to a higher level, the signal stored in the sampling capacitor 23 is transferred to a hold capacitor 25, and then is delivered to a signal electrode through an output circuit including a differential amplifier 26 and an output transistor 27.
In the circuit described above, when light is irradiated upon the IC driver 15, (1) the transistor 22 of the sampling pulse input section whose potential becomes high, and (2) the transistor 24 of the TRF signal input section becomes leaky owing to photo-electric effect. The leak causes a false display on the liquid crystal display device. The false display provides a problem particularly for liquid crystal display devices for projection TV where an intensified light is irradiated.